Ruby

Ruby is distinguished for its bright red color, being the most well known red gemstone. Beside for its bright color, it is a most desirable gem due to its hardness, durability, luster, and rarity. Transparent rubies of large sizes are even rarer than Diamonds. Ruby is the red variety of the mineral Corundum. Sapphire, the other gem variety of Corundum, encompasses all colors of Corundum aside from red. In essence, Ruby is a red Sapphire, since Ruby and Sapphire are identical in all properties except for color. However, because of the special allure and historical significance, Ruby has always been classified as an individual gemstone, and is never identified as a form of Sapphire (though some purplish-red colors may straddle the line of being classified as either Ruby or Sapphire).

Chemical Formula	Al2O3
Color	Red
Hardness	9
Crystal System	Hexagonal
Refractive Index	1.76Â -Â 1.77
SG	3.9Â -Â 4.1
Transparency	Transparent to opaque
Double Refraction	.0008
Luster	Vitreous to adamantine
Cleavage	None, but may exhibit parting
Mineral Class	Corundum